This invention relates to electronically controlled sewing machines of the type having a microcomputer for monitoring operator actuatable controls, retrieving pattern data from a memory, manipulating that data, and controlling the positioning of the needle and work piece during the sewing operation.
The use of microcomputers for controlling certain operations of a sewing machine has recently been proposed. Such use typically involves a single set of coded instructions resident in memory and being continuously executed by the microcomputer. A sync pulse is generated in timed relation with the needle and work feed mechanisms that is detected by the microcomputer thereby enabling the data output drivers to output bight and feed data to the servo systems for actuating the needle and work feed mechanisms. See, for example, U.S. Pat. No. 4,142,473, dated Mar. 6, 1979, to Itoh, which discloses an electronically controlled sewing machine including a microcomputer having the capability to produce any number of stitch patterns in the order in which they were selected by the operator. When the microcomputer is ready to output stitch data to the bight and feed servo systems, it enables a schmitt trigger which is arranged to pass a signal from an optical interruptor device to an input line of the microcomputer. The optical interruptor, comprising a light emitter and detector pair, produces signals in timed relation to the rotation of the armshaft. Once the schmitt trigger is enabled, the microcomputer will wait in a software loop continuously interrogating the input line until a signal is received from the optical interruptor at which time the bight or feed data is output to the appropriate servo. A serious problem associated with this arrangement is the inability of the microcomputer to adequately control the various functions of the sewing machine while waiting in the software loop should the armshaft rotation be temporarily slowed or stopped completely.
Additionally, see U.S. Pat. No. 4,280,424, dated July 28, 1981, to Carbonato et al, which discloses an electronically controlled sewing machine including a microcomputer having the capability to operate on stored stitch pattern data in response to input control signals from the keyboard for redefining the stitch pattern data. Carbonato utilizes a clock interruption scheme to divert execution from the main processing program to an interrupt routine for performing certain housekeeping tasks such as decrementing a clock counter and scanning the keyboard for operator actuated keys. Pattern data is retrieved for the selected pattern and appropriate initialization procedures are carried out. The main processing program then controls the sewing operation including output of stitch pattern data to the bight and feed servo systems. The microcomputer must continually interrogate input lines for the presence of bight and feed sync signals to assure correct timing of data output to the servos. This results in substantial wasted MC time. Further, the interrupt routine has no provision for refreshing the current status of the bight and feed servo systems thereby providing an opportunity for the bight and feed mechanisms to drift.